1. Field of the Invention
The present invention relates to roof and ground support apparatus and systems. Particularly, the present invention provides a cost-effective and disposable device to facilitate ground and roof control. This invention may be combined with a vehicle for transporting the yieldable props and for placing them.
2. Background of the Invention and Related Art
The present invention relates to a novel apparatus for providing roof and ground control in places such as mines, underground cavities, or any other place in which roof and floor are creeping together.
Different types of ground and roof control devices/props are known including those in U.S. Pat. Nos. 5,015,125, 5,215,411, 5,228,810, and the patents cited therein. U.S. Pat. Nos. 5,015,125, 5,215,411 and 5,228,810 rely on frictional forces between adjacent, tubular, overlapping telescoping members.
Other prior art systems include the installation of vertical timber posts or pairs of timber lengths stacked horizontally in quadratures, one pair on top of another. Devices known as doughnut cribbing comprising a series of vertically stacked reinforced concrete discs. All these support systems are used in underground mines at track turnout areas, track entry intersections, tailgate entries, at head gates, in mine drift tunnels and openings and at or near the mine face where excavation is occurring.
All of these systems do provide some yield. Some are costly and require significant transportation and installation costs. Others bear loads to a certain extent and then ultimately fail. Those constructed of wood have bearing strengths depending upon the nature of the wood and wood moisture.
Still other devices incorporate steel columns utilizing telescoping posts which provide varying load capabilities and yield, but are typically expensive.
Other types of yieldable roof support include roof mine bolts and associated brackets and nuts. When, for example, a mine roof begins to sag due to excavation, roof bolts, inserted into the roof of the mine tunnel to help support sections of the roof, are put under tensile stress. Due to Poission's ratio, the roof bolts are stretched slightly thinner. Depending upon the nature of the threads of the bolt, and any attached nuts or bearing plates or brackets, the bolt, its threads, any associated bearing plate or nuts, and their associated structures may deform permitting some yield to the sagging roof. In some cases, deformation of these devices results in the critical failure of the system with no additional support. DYWIDAG-Systems International USA, Inc. of Salt Lake City, Utah, has provided a nut with an inside thread diameter which changes from one end of the nut to the other end of the nut with receiving threads of correspondingly different depths relative to a roof bolt. This roof bolt nut permits incremental deformation or shearing of the roof bolt (a threaded bar) under load as the nut is pushed off the bolt, thus maintaining a resistive force against ceiling sag or floor thrust until the nut is pushed off the bolt.